This invention relates to the removal of ferric chloride from gases containing the same. The removal of ferric chloride from gases may be necessary or desirable for any of several reasons.
For instance, certain chlorinated hydrocarbons, such as chloroform, carbon tetrachloride, 1,2-dichloroethane and ethyl chloride, are frequently produced by oxychlorination of corresponding saturated or unsaturated aliphatic hydrocarbons and/or their chlorinated derivatives. Such processes are carried out by contacting the hydrocarbon (e.g. methane, ethane, ethylene) with or without the presence of chlorinated derivatives thereof, with hydrogen chloride and an oxygen-containing gas (usually air) in the presence of a catalyst. In many oxychlorination processes, the catalyst comprises cupric chloride, plus additives such as alkali metal chlorides and/or rare earth metal chlorides, on a porous support such as alumina, silica-alumina, diatomaceous earth, etc. Such a cupric chloride oxychlorination catalyst may contain as minor impurities, small amounts of iron, for example, up to about 800 ppm. These impurities may be in the form of ferric chloride and/or other iron compounds. Additional amounts of iron chlorides (ferric and/or ferrous chloride, which would be converted to ferric chloride in the oxychlorination zone) may be introduced into the catalyst in the hydrogen chloride stream, resulting from hydrogen chloride corrosion of steel equipment or conduit lines in the hydrogen chloride flow circuit. Even stainless steel may corrode to some extent. Similarly, corrosion of steel piping and/or other equipment in the air system would produce small amounts of iron oxides which could also be converted to ferric chloride in the oxychlorination zone. Though ferric chloride has been proposed as an oxychlorination catalyst, it has been found that its presence can be detrimental to the performance of a cupric chloride catalyst in such a process, in that the presence of ferric chloride can result in catalyst disintegration and/or deactivation. These can result, for instance, in pressure drop increases, catalyst attrition due to formation of dust or catalyst fines, and a general shortening of catalyst life and lowering of activity. As small an increase as 0.1% of ferric chloride content in the catalyst (over such impurities as may be present) can have a deleterious effect on a cupric chloride catalyst which has otherwise been found satisfactory for oxychlorination reactions. The problem can be generally circumvented by fabricating the gaseous feed piping circuit and associated equipment from relatively noncorrosive materials such as nickel; however, this can be expensive, especially for large-volume equipment.
In other environments, various gases may contain amounts of ferric chloride resulting, for example, from corrosion of steel equipment, entrainment of ferric chloride particles in processes using ferric chloride catalysts, steel-making processes, etc. Depending on the particular process involved, it may be desired either to purify a gas containing ferric chloride so as to obtain a purified product or to remove the ferric chloride in order to prevent problems downstream of its introduction into the system.
Ferric chloride may also be present in process gases in the production of chlorides of metals such as titanium, tantalum, niobium and hafnium from ores containing iron compounds in addition to compounds of the desired metals. One process for removing ferric chloride from a gaseous mixture of metal chlorides is described in U.S. Pat. No. 3,066,010, and consists of passing the gases through a bed of hot rock salt. Ferric chloride forms a complex with the sodium chloride; the rock salt is heated to a temperature above the melting point of the complex (specifically 250.degree.-450.degree. C) to permit removal of the complex in molten form.
It is an object of the present invention to provide a process for the purification of gases containing ferric chloride.
A further object of the present invention is to provide a process for the purification of gases containing minor amounts of ferric chloride.
A still further object of the present invention is to provide a process for the removal of ferric chloride from hydrogen chloride gases.
Yet a further object of the present invention is to provide a process for the prevention of ferric chloride contamination of cupric chloride oxychlorination catalysts.